The evolution and future direction of the treatment pattern of advanced liver cancer

Hepatocellular carcinoma is one of the
most common solid tumors.
A large proportion of patients with hepatocellular carcinoma are diagnosed with advanced stage and can only receive systemic therapy
.
We have witnessed the evolution
of systemic therapies from single-drug targeted therapies (Sorafenib and lenvatinib) to checkpoint inhibitors + targeted therapies (Atezolizumab + Bevacizumab).
Despite significant progress, only a small percentage of patients can achieve lasting clinical benefits, so significant treatment opportunities and challenges
remain.
Over the past few years, emerging systemic therapies, including new molecularly targeted monotherapies (e.
g.
, donafenib), new immuno-tumor monotherapies (e.
g.
, durvalumab), and new combination therapies (e.
g.
, durvalumab + tremelimumab), have shown excellent efficacy
in clinical trials.
In addition, many new treatments have been proposed and developed, such as sequential combination targeted therapy and next-generation cell therapy, which also have the potential to improve the treatment outcomes
of patients with advanced liver cancer.
In this article, we will briefly introduce
the evolution and future direction of advanced liver cancer treatment.

The current treatment landscape

In the past, chemotherapy drugs were the main drugs for the systematic treatment of advanced liver cancer, with limited efficacy and significant adverse effects
.
In 2007, the FDA approved the multi-target tyrosine kinase inhibitor (TKI) sorafenib, the first targeted drug to be proven effective in patients with advanced liver cancer, and has been the standard drug for the treatment of advanced liver cancer for more than a decade, which has greatly changed the treatment model of liver cancer patients (Figure 1).

However, the therapeutic effect is far from satisfactory
.
Sorafenib improved the survival advantage
by only 2.
8 months compared to placebo.

Figure 1.
Systemic therapy for the treatment of advanced liver cancer

The paradigm shift in first-line therapy highlights the need to
rethink the outlook for second-line therapy.
Currently approved second-line therapies, including regorafenib, cabozantinib, ramucirumab, pembrolizumab, and combinations of nivolumab and ipilimumab, have only been evaluated as effective in patients who have previously received sorafenib, but none have been shown effective after the failure of the atezolizumab–bevacizumab combination
。

Nivolumab (anti-PD1 monoclonal antibody) and ipilimumab (anti-CTLA4 monoclonal antibody) are the first dual immunotherapy combination regimens approved for patients with advanced liver cancer after first-line therapy failure
.
A subcohort result from the CheckMate trial showed that the combination of nivolumab and ipilimumab produced an excellent ORR
of approximately 30 percent in patients previously treated with sorafenib.
The combination of nivolumab and ipilimumab appears to be associated with
higher response rates compared to ICB monotherapy.
However, it remains to be determined
whether this excellent response to treatment translates into improvements in overall survival.
The effectiveness of other ICBs as second-line therapy remains unclear
for patients receiving first-line ICBs.

Emerging targeted monotherapies

Targeted therapy aims to inhibit molecular pathways that are essential for tumor growth and maintenance, and is currently the main treatment
for advanced liver cancer.
Emerging targeted therapies for hepatocellular carcinoma can be divided into two categories: new multi-kinase inhibitors with similar mechanisms of action as before, and small molecule drugs
with more specific targets.

Donafinib is a multikinase inhibitor
similar to sorafenib.
Essentially, it is a modified form of sorafenib with an improved pharmacokinetic profile (including an extended half-life and reduced clearance).

In a phase III ZGDH3 III trial conducted in China involving 668 patients with advanced liver cancer, Donafinib had a statistically significant improvement
in overall survival compared to sorafenib alone.
In randomized controlled trials, no other first-line monotherapy has so far shown significant superiority over sorafenib except donafenib
.
Apatinib is another multi-kinase inhibitor with high selectivity
for VEGFR2.
The phase III AHELP trial in China included 400 patients
with intermediate and advanced liver cancer who underwent systemic chemotherapy or targeted therapy.
The results showed that Apatinib had a significant advantage in overall survival in these patients compared to placebo (Table 1).

Table 1.
A drug with positive results in a phase III clinical trial for advanced liver cancer

Table 2.
Clinical progress of liver cancer treatment drugs with single targeted therapy

The fibroblast growth factor family includes at least 5 FGFRs (FGFR1 to FGFR5) and 22 homologous ligands
.
Among these receptors, FGFR4 is the one predominantly expressed in the human liver and is therefore considered a potential target for the treatment of
liver cancer.
Its endogenous ligand FGF19 binds to FGFR4 to activate downstream pathways and promote cell proliferation
.
Fisogatinib is a selective FGFR4 inhibitor
.
In the Phase I study, 98 patients with advanced liver cancer were divided into FGF19+ and FGF19- groups and treated with Fisogatinib
.
Interestingly, the ORRs of the FGF19+ and FGF19- groups were 17% and 0%,
respectively.
This study shows that FGF19 can serve as a potential predictive biomarker for the use of FGFR4 inhibitors
.

The TGF-β pathway has a dual role
in the development of tumors.
Although it can initially inhibit proliferation, it can act as a tumor promoter in the later stages of carcinogenesis, promoting cell invasion and metastasis
.
In a study involving 149 patients, the TGF-βR1 inhibitor galunisertib was investigated as a second-line treatment for liver cancer
.
After treatment with galunisertib, the median overall survival of patients with high and low serum alpha-fetoprotein levels was 7.
3 months and 16.
8 months
, respectively.
This provides a mechanistic basis
for alpha-fetoprotein as a biomarker for TGF-β inhibition.

The PI3K-AKT-mTOR pathway is another important signaling pathway
in the development and development of liver cancer.
This pathway has been reported to activate
abnormally in ~50% of liver cancer cells.
So far, several mTOR inhibitors, such as everolimus and temsirolimus, have been proposed as monotherapy for liver cancer, but have failed in clinical trials
.
Several new mTOR inhibitors have broader inhibitory effects in the PI3K-AKT-mTOR pathway, including dual mTORC1-mTORC2 inhibitors and PI3K-mTOR inhibitors (e.
g.
, onatasertib), which are currently in early-stage clinical trials
for advanced liver cancer.

Emerging immunomonotherapies for tumors

The liver contains many immune cells such as Kupffer cells (hepato-resident macrophages), dendritic cells, and lymphocytes
.
In response to foreign molecules, the liver typically maintains an anti-inflammatory environment by expressing and secreting inhibitory molecules, including IDO1, PDL1, and TGF-β
.
Similarly, hepatocellular carcinoma presents an inflammatory but suppressed immune environment, making patients with hepatocellular carcinoma ideal candidates
for immunotherapy.
In clinical trials, many immuno-oncology drugs have been evaluated as monotherapies for the treatment of liver cancer (Table 3).

These drugs can be divided into two categories: novel ICB drugs that target successful targets such as PD1/PDL1 or CTLA4, and novel drugs
that target other immunomodulatory molecules.

Table 3.
Clinical progress of liver cancer treatment drugs with single tumor immunotherapy

Although targeting the same targets as nivolumab and pembrolizumab, camrelizumab and tislelizumab have some different characteristics
.
For example, unlike nivolumab and pembrolizumab, where camrelizumab has different binding epitopes, tislelizumab has the unique ability to
avoid ADCPs.
The results of the phase I/II study suggest that in second-line trials, their clinical efficacy is broadly similar
to nivolumab and pembrolizumab.
Compared to sorafenib, Tislelizumab is currently being evaluated in a Phase III clinical trial of RATIONALE-301 as a first-line therapy, and the results of the trial will be published soon (NCT03412773).

Durvalumab is an anti-PDL1 monoclonal antibody that has been shown to be clinically active and tolerated
in advanced liver cancer in a second-line setting in phase II studies.
Its effectiveness in first-line settings has been evaluated in HIMALAYA Phase III trials, with non-inferior targets for overall survival compared to sorafenib
.
Patients treated with durvalumab also had fewer grade 3 or 4 treatment-related adverse events (TRAEs) than those treated with sorafenib (12.
9% versus 36.
9%)
.
Taken together, the results of these trials suggest that immunotherapy alone may also be a promising first-line treatment option for patients with liver cancer, particularly for those who require a safer regimen
.

In addition to PD1-PDL1 or CTLA4 inhibition, significant progress
has been made in inhibitors against other immunosuppressive molecules such as TIM3, LAG3, TIGIT and IDO1 and agonists against co-stimulatory molecules such as CD40, OX40.
Some of these drugs have already entered clinical development, and some preliminary results have been published
.

Emerging combination therapies

Extensive clinical evidence suggests that monotherapy is associated with the development of drug resistance and provides only limited clinical benefit
.
In contrast, combination therapies can overcome drug resistance and are more likely to be clinically effective
.
Currently, there are few combination treatment options for liver cancer, suggesting considerable opportunities and challenges in this area (Figure 2).

Figure 2.
Combination therapy for the treatment of liver cancer

• Combination of molecularly targeted drugs

The combination of molecularly targeted drugs can achieve synergistic effects
by targeting multiple key components within the cell.
Although this combination therapy is conceptually superior to monotherapy, no substantial clinical success
has been achieved so far.

Some new combinations, such as lenvatinib plus the EGFR inhibitor gefitinib, have yielded promising results
in early clinical trials.
By blocking feedback activation of EGFR-PAK2-ERK5 signaling, the combination of Lenvatinib and Gefitinib resulted in a treatment response in approximately one-third of patients with EGFR+ liver cancer
.
Therefore, the use of EGFR overexpression as a biomarker may allow more patients with advanced hepatocellular carcinoma to benefit
from this treatment.

Currently, there is a limited
number of molecularly targeted drug combinations used in clinical studies for the treatment of hepatocellular carcinoma.
Targeted combination therapies tend to have higher toxicity and lower likelihood
of lasting effectiveness than ICB-based combination therapies.
Nevertheless, combination targeted therapy still has an irreplaceable role in the treatment of liver cancer, because patients with certain contraindications, such as autoimmune diseases and a history of organ transplantation, are not suitable for ICB therapy
.

• Combinations of immuno-oncology drugs

The mechanisms of action of immuno-oncology drugs vary widely, providing opportunities
to develop immunotherapy combinations.
At present, PD1-PDL1 inhibitor + CTLA4 inhibitor is the most studied immuno-oncology combination
of hepatocellular carcinoma.
Inhibition of PD1-PDL1 can enhance the antitumor activity of effector T cells, while inhibition of CTLA4 can increase the abundance of CD4+ and CD8+ T cells within
tumors.
If effector T cells are not present in tumor tissue, inhibition of PD1-PDL1 alone does not induce a potent antitumor response, therefore, simultaneous inhibition of CTLA4 may be required to ensure antitumor activity
.
ACCORDING TO THIS PHILOSOPHY, IN THE PHASE III HIMALAYA TRIAL, WHICH INCLUDED 782 PATIENTS WITH ADVANCED LIVER CANCER, THE COMBINATION OF DUVALUMAB AND TEMLIMUMAB AS FIRST-LINE THERAPY SHOWED SIGNIFICANT EFFICACY, SIGNIFICANTLY IMPROVING OVERALL SURVIVAL
.

Many immuno-oncology drugs can target other immunomodulatory molecules such as TIM3, LAG3, TIGIT, IDO1, and CD40
.
They modulate the immune response through different mechanisms of inhibition of PD1-PDL1 or CTLA4 and, therefore, can produce synergistic and complementary effects to treat tumors
.
In March 2022, the combination of LAG3 inhibitors relatlimab and nivolumab was approved by the FDA for the treatment of melanoma, which is an important milestone
in the development of tumor immunodrugs.
This success reveals great potential
beyond combinations of PD1-PDL1 or CTLA4 inhibition.
Several such new combinations, including nivolumab plus relatlimab (NCT04567615), are currently being studied in clinical studies to treat liver cancer
.

• Combined use of ICB with VEGF–VEGFR antibodies

Angiogenesis is a hallmark of cancer and has been widely shown to be associated with
cancer progression and metastasis.
Abnormal tumor angiogenesis driven by vascular endothelial growth factor can lead to the formation
of immunosuppressive factor TME.
Selective inhibition of this process using an anti-VEGFA monoclonal antibody (e.
g.
, bevacizumab) or an anti-VEGFR monoclonal antibody (e.
g.
, Ramucirumab) can reshape the microenvironment through a variety of mechanisms, including promoting the maturation of dendritic cells, changing the M1:M2 macrophage ratio, reducing the aggregation of Treg, increasing the abundance of cytotoxic T cells, thereby weakening their immunosuppressive effects
.

In addition to the approved atezolizumab–bevacizumab combination, there are other combinations with similar mechanisms of action for the treatment of advanced liver cancer
.
In the phase III Orient-32 trial, the combined efficacy
of sintilimab (anti-PD1) and the bevacizumab biosimilar IBI305 was evaluated in 571 patients with advanced liver cancer in the first-line setting.
Patients who received this combination regimen had statistically significant benefits
in both overall survival and progression-free survival compared with patients receiving sorafenib alone.

• Combined use of ICB and multikinase inhibitors

Currently, four multikinase inhibitors are approved for the treatment of liver cancer, all of which can exert antiangiogenic effects
by inhibiting VEGFRs.
Therefore, their immunomodulatory function is similar to that of anti-vascular endothelial growth factor antibodies
.
Since MAK inhibitors can target other molecules such as PDGFR, FGFRs, KIT, and METs, they also have an additional effect on tumor immunity and do not depend on vascular endothelial growth factor inhibition
.
In addition, polykinase inhibitors are thought to have relatively stronger tumor-killing and tumor-necrotic activity
compared to antiangiogenic drugs.
Therefore, they may induce the release of more tumor antigens, thereby enhancing the immunogenicity
of tumors.

All four polykinase inhibitors have been evaluated for their synergistic potential with ICBs, with lenvatinib
being the most studied.
In the Phase Ib Keynote-524 study, the ORR of the combination of lenvatinib and pembrolizumab was 36.
0% in 104 patients with advanced liver cancer who did not receive systemic therapy, which was twice that of pembrolizumab alone in the Keynote-224 study
.
Based on these excellent effects, a phase III LEAP-002 trial comparing this combination with sorafenib in patients not receiving systemic therapy has been initiated
.

Unmet needs and future directions

• Look for biomarkers for patient selection

Current systemic therapies have shown highly heterogeneous efficacy in patients with advanced liver cancer, so the identification of biomarkers for prediction and patient selection has become an urgent need
.

In response to sorafenib, the mutational state of the PI3K-AKT-mTOR pathway was identified as a genomic biomarker; Patients with associated mutations tend to have lower ORR and shorter OS and PFS
.
In addition, ACSL4 expression and VEGFA amplification have also been shown to predict the response to sorafenib
.
For Lenvatinib, several serum biomarkers, including VEGF, ANG2, FGF21, and FGFR4, have shown potential predictive power
in clinical studies.
In addition, studies of second-line TKIs regorafenib and cabozantinib have yielded some promising biomarkers, including several serum microRNAs (such as MIR30A and MIR122) and serum AFPs
.

For ICB therapy, candidate biomarkers can be divided into four categories: immunohistochemical marker biomarkers, genomic biomarkers, transcriptional biomarkers, and others
.
Previous immunohistochemical markers for hepatocellular carcinoma include PD1, PDL1, CD3, CD4, CD8, CD68, CD163, and FOXP3
.
Overall, PD1, PDL1, CD3, and CD8 were found to have some predictive power, while other survival benefits associated with ICB were not related
.
Tumor mutational burden (TMB) is the most studied genomic biomarker, showing predictive power
in a variety of tumors such as melanoma, non-small cell lung cancer, and bladder cancer.
However, one study claimed that TMB was only effective in tumors where CD8+ T cell abundance was positively correlated with neoantigens, and liver cancer was not one
of them.
Mutations in the Wnt-β-Catenin pathway are another potential genomic biomarker
.
HCCA carrying CTNNB1 mutations is often associated with the immune rejection phenotype, which is characterized by low immunopenetration and reduced cytolytic activity
.
These tumors are more likely to be ineffective against
ICB treatment.
In addition, studies involving transcriptional biomarkers and other biomarkers, such as circulating tumor cells and circulating tumor DNA, have also revealed some potential candidate biomarkers for predicting immunotherapy response for liver cancer
.

• Target the drivers of "undruggable"

Currently, the major mutational drivers in hepatocellular carcinoma, including telomerase reverse transcriptase promoter (TERTp), CTNNB1 (encoding β-catenin), and TP53, remain "undruggable
.
" The TERTp gene is the most commonly mutated gene in hepatocellular carcinoma, found in about 60% of hepatocellular carcinoma, and has been reported to be strongly associated
with the development of progressive HCC.
TERT encodes a catalytic protein subunit of telomerase that plays a crucial role
in telomere maintenance.
Cells without telomere maintenance mechanisms gradually suffer telomere wear, eventually triggering replicable aging or apoptosis
.
The maintenance of telomeres enables cells to overcome replicative death, thus opening up the possibility
for their therapeutic development.
In a preclinical study of liver cancer, silence of TERT expression with antisense oligonucleotides in human hepatoma cell lines and xenograft mouse models resulted in proliferation arrest and death of tumor cells, which provides preliminary evidence
for inhibiting the therapeutic potential of TERT in liver cancer.

Nearly 50% of liver cancers exhibit activation
of the Wnt-β-Catenin signaling pathway due to mutations in the CTNNB1, AXIN1, or APC genes.
Drugs that target upstream molecules of Wnt-β-Catenin signaling, such as AXIN and LRP, such as salinomycin and NVP-TNKS656, have been developed and tested in preclinical models of multiple tumor types, including liver cancer, and have shown efficacy
.
However, these drugs may be ineffective
when the Wnt-β-Catenin signaling pathway is activated downstream.

Another gene that is often altered in hepatocellular carcinoma is TP53, which codes for the tumor suppressor gene P53
.
Unlike mutations in the TERT promoter or CTNNB1, mutations in TP53 usually result in loss
of gene function.
Therefore, targeting TP53-mutated liver cancer is challenging, and a study published in 2021 showed that it is possible
to treat TP53-mutated tumors by reactivating the mutated p53 protein.
In mouse NSCLC xenograft models, arsenic trioxide (ATO) treatment significantly inhibited the growth of TP53-mutant tumors, suggesting that ATO could be a potential therapy
for patients with TP53-mutant tumors.
In addition to reactivating P53, there are other therapeutic strategies to combat this mutation, such as reintroducing wild-type P53 into cancer cells, targeting its regulators, such as MDM2
.

• Explore new strategies based on targeted therapies

Over the past few years, many innovative targeted therapy strategies
for liver cancer treatment have emerged.
A typical example is sequential combination therapy, where therapeutic drugs are administered sequentially and the first drug can induce weakness in cancer cells, making them more susceptible to the second drug (Figure 3).

Sequential combinations can result in lower combination toxicity compared to conventional combinations administered simultaneously, but still maintain synergistic antitumor effects
.
One successful application of this concept is the "one-two punch" therapy, which has been shown to be feasible
in the treatment of liver cancer.

Figure 3.
Schematic diagram of sequential combination therapy

• Expand existing immunotherapy approaches

The therapeutic potential of immunotherapies other than ICI for hepatocellular carcinoma has also been extensively studied
.
Adoptive cell therapy (ACT) is the most representative non-ICB immunotherapy available, which is able to enhance the anti-tumor immune response
by infusing immune cells from the patient's own or healthy donors.
Previous attempts to use ACT for liver cancer have included transfusions of lymphokine-activated killer cells, cytokine-induced killer cells, and tumor-infiltrating lymphocytes
.
At present, CAR-T cell therapy and TCR-T cell therapy have become hot
spots in ACT therapy for liver cancer.
A variety of CAR T-cell therapies (targeting GPC3, CD147 or NKG2DL) and TCRT cell therapies (targeting AFP or hepatitis B virus antigen) are in clinical trials for the treatment of liver cancer with some excellent preliminary results
.

The use of therapeutic vaccines is an attractive strategy aimed at inducing or enhancing specific immune responses
against tumor antigens.
These vaccines include peptide vaccines, dendritic cell vaccines, and oncolytic viruses
.
Based on well-defined tumor-associated antigens such as AFP, GPC3, and multidrug resistance-associated protein 3 (MRP3), peptide vaccines
against liver cancer have been developed.
Dendritic cell-based vaccines can be produced
by inducing the activation and maturation of dendritic cells in vitro using specific antigens, including peptides, proteins, nucleic acids, and lysates.
Oncolytic viruses are engineered viruses that selectively lyse tumor cells
.
Oncolytic-mediated oncolysis not only leads to tumor regression, but also enhances the anti-tumor immune response
by releasing soluble tumor antigens.
Although therapeutic vaccines are not new, some of which have been trialled as monotherapies in liver cancer for several years, their combination with new ICB therapies has yielded early and promising results and therefore warrants further study
.

BsAb represents an emerging immunotherapy with the ability to
mediate unique biological effects that cannot be achieved with traditional monospecific antibodies.
BsAbs can be used as T cell redirecting molecules (such as EpCAM-CD3 BsAbs), tumor-targeted immunomodulators (such as tumor anti-CD40 BsAbs) or dual immunomodulators (such as PD1-CTLA4 BsAbs) to enhance the killing effect
of immune cells on tumor cells.
BsAb has many advantages
.
For example, in preclinical testing of novel transgenic mouse models expressing human PD1 and CTLA4, PD1-CTLA4 BsAb MEDI5752 demonstrated higher efficacy while limiting toxicity
compared to conventional monoclonal antibody combinations against PD1 and CTLA4.
BsAbs developed for liver cancer, such as GPC3-CD3 and PD1-CTLA4 BsAbs, have also shown excellent early results
in preclinical and clinical studies.

The treatment of liver cancer is advancing
at an alarming rate.
Standard therapies have evolved from single drug TKIs to a combination of ICB and targeted drug therapies, significantly improving patient survival benefits
.
At present, some new therapies for the treatment of advanced liver cancer are undergoing clinical research, which can be divided into three main categories, including molecularly targeted monotherapy, tumor immunomonotherapy and combination therapy
.
Some of these drugs, such as donafenib, apatinib, durvalumab, and combinations of durvalumab and tremelimumab, have achieved excellent results in phase III clinical trials, providing more potential treatment options
for patients with advanced liver cancer.
In addition, preclinical studies have proposed a number of new treatments, including targeted therapies (e.
g.
, sequential combination therapy) and immunotherapy (e.
g.
, next-generation ACT), which have the potential to further improve the treatment outcomes
of liver cancer in the future.

1. Evolving therapeutic landscape of advanced hepatocellular carcinoma.
   
2. Immunotherapies for hepatocellular carcinoma.
   
3. Molecular therapies and precision medicine for hepatocellular carcinoma.